In recent years, laser devices including semiconductor laser (also called “laser diode (LD)”) elements have been commercialized and used in the optical communication field. In such a laser device, (i) a semiconductor laser element and an optical fiber are optically coupled with each other with a high optical coupling efficiency, and (ii) laser light, which is emitted by the semiconductor laser element, enters the optical fiber via an end part of the optical fiber.
In such a laser device, a laser light emission surface of the semiconductor laser element is precisely aligned with respect to the end part of the optical fiber so that the laser light emitted by the semiconductor laser element enters the optical fiber as much as possible. Further, it is important to maintain the aligned state.
For example, Patent Literature 1 discloses a laser diode assembly as a laser device which includes a semiconductor laser element and an optical fiber. In the laser diode assembly, a laser diode chip (here, referred to as “semiconductor laser element”) and an optical fiber are provided on a base.
The semiconductor laser element and the optical fiber are fixed to the base by soldering, whereby an aligned state of a laser light emission surface of the semiconductor laser element and an end part of the optical fiber is maintained.
Particularly, in a case of a laser device which is required to have high light intensity, a multi-mode semiconductor laser element, which oscillates in a plurality of waveguide modes, is employed as a light source. The multi-mode semiconductor laser element emits light from an end of waveguide whose width falls within a range between 10 micrometers and several hundred micrometers.
In general, a spread angle of laser light emitted from such a multi-mode semiconductor laser element is approximately 40°, in terms of FWHM (Full Width at Half Maximum) in a vertical direction (perpendicular to an active layer of the semiconductor laser element) on the laser light emission surface. Moreover, in general, an FWHM angle of the laser light in a horizontal direction on the laser light emission surface becomes approximately 10° (for example, see Non Patent Literatures 1 and 2). That is, the laser light spreads more widely in the vertical direction than in the horizontal direction.
Under the circumstances, in general, the end part of the optical fiber is formed into a wedge shape so that the end part has a lens function (see Non Patent Literatures 1 and 2). This allows the laser light, which spreads widely in the vertical direction, to be efficiently optically coupled with the optical fiber, and accordingly a larger amount of laser light can be caused to enter a core part of the optical fiber.